Having two delayed children, with one being profoundly so, has got to be incredibly stressful. My son has had delays as well, fortunately not profound, but I know how stressful that can be. So having a both has got to be incredibly tough.
All the advice is great but ultimately you need to find what works beat for you. Are you and the misses ever able to just get away just the two of you, even just for a weekend? I know this might be difficult with the family situation but getting a regularly scheduled break can give you something to look forward to and help take some of the stress away.
If the two of you can't get away together, try the same plan but with each of you taking turns getting away for a weekend with friends. Or even just a full day away with friends. I would assume the wife is a bit stressed too.
Good luck finding out what works for you.